This invention relates to an ultrasound transducer using stacked piezoelectric composites and method for stacking the transducer. In particular, a method for aligning layers of piezoelectric composite material is provided.
Stacked piezoelectric composite transducers provide improved electrical matching. Broader bandwidth and increased sensitivity may also be provided. Examples of stacked transducers are disclosed in U.S. Pat. No. 6,121,718 (Ser. No. 09/052,776, filed Mar. 31, 1998) and U.S. Pat. No. 5,957,851, the disclosures of which are incorporated herein by reference. Stacked transducers have also been used in commercial embodiments, such as the Acuson S2 transducer.
Medical ultrasound imaging transducers use piezoelectric materials to convert between acoustic and electrical energies. Some piezoelectric materials provide for increased bandwidth and sensitivity as compared to other materials. For example, a 1-3 composite of piezoelectric material extending in one dimension and a bonding polymer extending along three dimensions is commonly used. Such composites have a higher Kt than many other piezoelectric materials or composites. The composites may also be formed into various shapes, increasing the options for window materials and versatility of transducer design.
Using composite materials for stacked transducers requires alignment between the ceramic phase of each layer. An accuracy in the order of xc2x10.0002 inches is desired. Misalignment results in decreased function of the transducer. If a monolithic stacked ceramic is diced in the elevational dimension to form the composite, the electrical connections are difficult to manage. For practical implementation, the composite microstructure of piezoelectric material within a polymer is generated before the layers are glued together, requiring the precise alignment discussed above.
One method developed for aligning stacked layers of composite materials uses fiduciaries. Fiduciaries or reference holes are placed in the ends of the individual layers. The fiduciaries are aligned while the layers are stacked. However, the desired accuracy is often not consistently provided.
Using a composite layer coupled to a monolithic layer avoids alignment problems. In particular, a 1-3 composite is stacked on a layer of non-composite piezoelectric material. The electrical contacts are manageable where dicing is performed after the plates are glued together. However, this method does not allow forming the transducer into non-planar shapes. Furthermore, the performance advantages of 1-3 composites are limited by this method of alignment.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiment described below includes a transducer and using stacked composites and a method for making the transducer. A plurality of indentations are provided on a first layer of composite material, such as associated with etching away piezoelectric material posts (i.e. ceramic phase) relative to a polymer (i.e. epoxy phase). A respective plurality of protrusions are provided on a second layer of composite material, such as associated with etching away the epoxy phase relative to the ceramic phase. The protrusions insert into the indentations, aligning the two layers.
In a first aspect, an ultrasound transducer for converting between electrical and acoustic signals is provided. The transducer comprises a first layer of piezoelectric material. The first layer comprises at least one indentation. A second layer of piezoelectric material is provided. The second layer includes at least one protrusion. The protrusion is adapted for insertion into the indentation.
In a second aspect, a method of manufacturing an ultrasound transducer is provided. At least one indentation is created on a first layer of piezoelectric material. At least one protrusion is created on a second layer of piezoelectric material. The protrusion is inserted into the indentation.
In a third aspect, an ultrasound transducer for converting between electrical and acoustical signals is provided. A first layer comprises a plurality of extensions. A second layer comprises a plurality of receptacles. The receptacles align with the extensions.
Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments.